How To Get Rid Of Mold Growth On Germinating Seeds, Seedlings & Seed Starter Pots

Finding mold on seedlings is frustrating! In this post, I’ll show you step-by-step how to get rid of mold growing on your germinating seeds, starts, soil, and pots, and prevent it from coming back.

When mold starts growing on your carefully cultivated seedlings, it can be very disheartening.

It’s definitely one of the most annoying things about caring for seedlings, and something I get asked about a lot. But the good news is that it’s easy to fix!

Unfortunately, mold growth on seedlings, inside of seed starter trays, or on the pots can be a common problem. No matter what your experience level, you’re sure to run into this at some point.

The best thing you can do is to catch it early, and take steps to prevent it from growing in the first place. Keep reading to learn how to get rid of mold on your germinating seeds and new growth starts.

Why Are My Seedlings Molding?

We all know that mold thrives in a warm, damp environment. Well, those are the exact conditions that many seeds like to sprout in!

So, if we’re not careful, our seed trays can become the perfect breeding ground for all kinds of mold and mildew: white and fuzzy, green, yellow, or orange.

It’s scary to discover you have moldy seedlings for the first time! But don’t worry, it’s a problem that’s easy to fix with a few small changes.

Will Mold Hurt My Seedlings?

The good news is that the mold itself will not kill your seedlings. However, it is a sure sign that something else is wrong, and needs to be fixed ASAP.

Because what could eventually kill them is what causes the mold to grow in your seed trays in the first place.

The main causes are overwatering, improper ventilation, too much heat, and/or overcrowding. All of which I’ll talk about in detail below.

How To Get Rid Of Mold On Seedlings

The good news is that it’s easy to get rid of the mold growing in your seedling trays, and you don’t need to buy any chemical sprays or powders. Simply follow these steps…

Step 1: Remove the mold – The first thing you should do is carefully scrape or pull it off the top of the soil. I know, this sounds like a really disgusting job, but it’s very effective.

I use a sharp pencil or a small knife to gently get as much of the mold off the soil as I can, and wipe it into a paper towel.

Don’t worry if you don’t get every single bit off the soil, or if you’re too squeamish to do this part. Once you follow the remaining steps, the rest of it will die off on its own. Scraping it off just helps to get rid of it faster.

Step 2: Ventilate your flats – If the lids are still on your trays or flats, this is definitely part of the problem.

I usually try to keep the lids on my trays until the seedlings get tall. But if mold starts to grow, then it’s time to ventilate them.

Use a pencil or other similar item to prop open one end of the lid to get some fresh air into your trays. If all of your seeds have germinated, then you can just remove the lid completely.

Step 3: Allow the soil to dry out a bit – It’s important to make sure you’re not overwatering. The soil should never be soggy, and any excess water should be dumped out after 30 minutes.

Ideally, try to keep soil evenly moist, allowing the top part to dry out slightly between waterings. Never let it dry out completely though.

Consistent overwatering not only causes mold growth, but it will eventually kill the seedlings. So always check it before watering to ensure you’re not giving them too much. An inexpensive moisture gauge really comes in hand here.

Step 4: Turn off the bottom heat – Once all of the seeds have germinated, it’s best to turn off the heat mat. Too much heat will encourage mold to grow, and can also harm your seedlings.

How To Stop Mold From Growing In Your Trays

Taking the steps above will get rid of existing the mold, but it can come back at any time.

To stop it from growing again, you need to maintain an environment where seedlings will thrive, but mold and mildew won’t.

It can be a bit of a balancing act, but you’ll get the hang of it in no time. Here’s how to it from coming back…

Air Circulation

Providing good airflow is the first defense. Keep an oscillating fan gently blowing and rotating over your trays during the day.

This airflow also has the added benefit of strengthening the tiny starts too. Keep a close eye on the moisture level though, because the fan will dry the soil out much faster.

Water From The Bottom

Another great way to prevent mold growth is to water your seedlings from the bottom, rather than pouring it over the top.

Doing this makes it much easier to keep the top layer of soil dry, while ensuring the roots are getting enough moisture. Just make sure to pour out any water that hasn’t been soaked up after 30 minutes.

Thin Them Out

Like I mentioned above, it’s very important that your flats get good airflow. Overcrowded seedlings can prevent proper circulation, which means the mold will likely grow back.

So, if yours are overcrowded, but too small to pot up, then you need to thin them out to give them plenty of room to grow.

Pot Them Up

If you don’t have the heart to thin them, pot them up instead. You can repot seedlings once they are twice as tall as the original container.

This makes it much easier to maintain proper soil moisture, and prevent future mold growth on your seedlings.

I like to use plantable pots to make transplanting everything a snap. But you can use plastic ones, if you prefer, or if you have problems with mold on biodegradable pots.

Add Lighting

Proper seedling lighting will also help prevent the regrowth of mold. Position a grow lamp so it always hangs a few inches above your starts, and give them 14-16 hours of light every day.

Plugging your fixture into an inexpensive outlet timer makes it easy. You can buy a grow light kit, or make your own DIY grow lights for seedlings.

How To Prevent Mold On Seedlings

Now that you know how to get rid of mold growing in your seed trays, let’s talk about how we can prevent this from happening in the first place.

Use The Right Soil

It’s extremely important to use the right type of soil in your seed trays. Regular potting soil is too heavy for seedlings, and can cause a whole bunch of problems (including mold growth).

Make sure to use a lightweight, and fast draining soilless medium that is specifically made for growing seeds. Or you can try to make your own mix.

Disinfect Your Containers

Mold spores can lay dormant in dirty trays, and regrow year after year. So, it’s always a good idea to wash and disinfect your equipment between uses.

This is the best way to prevent any type of mold, mildew, or fungus, including seedling blight (which causes damping off), so don’t skip this step.

Use The Proper Equipment

If you’re just starting out, it’s so much easier to be successful when you use supplies and equipment that are specifically made for starting seeds.

I know this means spending a few extra dollars. But in the end, it’s worth the cost to avoid the frustration (and added expense) of losing all of your seedlings.

Finding mold growing on seedlings, the soil, or biodegradable pots and pods can be very scary and frustrating. It’s good to know that this problem is easily fixable by simply following the steps above.

If you need more help and guidance, you should take my online Seed Starting Course. It’s a self-paced, comprehensive online course that will walk you through step-by-step, show you exactly how to grow garden seeds, and care for your seedlings. Enroll and get started today!

Want to learn more about planting seeds indoors? Then pick up a copy of my Starting Seeds Indoors eBook. It’s a quick-start guide for beginners, or those anyone just looking for a refresher.

More Seedling Posts You Might Like

• When & How To Transplant Seedlings Into The Garden
• How To Harden Off Seedlings

Share your tips for controlling and getting rid of mold on seedlings in the comments below.